Method and arrangement for coupling messages in a central control device with decentralized communications devices

ABSTRACT

The invention describes a novel private branch exchange and the migration solution with respect to existing devices. Communication connections are established via a transport network, the control takes place in a centralized manner by means of a central control device, which is connected to the decentralized switching devices and the interface modules via a two-stage connection, a collection and distribution of the control messages being carried out in a decentralized manner and the control connection from the respective decentralized device to the central control being provided by an ATM network or an Ethernet connection.

CLAIM FOR PRIORITY

This application claims priority to International Application No.PCT/DE00/03175 which was published in the German language on Sep. 13,2000.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method and an arrangement for transportingmessages, and in particular, to control messages, in a switching devicesuch as a private branch exchange set up over a large area, in which anumber of decentralized devices are controlled from a central device.

BACKGROUND OF THE INVENTION

The requirements imposed on communication infrastructure installations,such as private branch exchanges for example, are constantly increasing.The cause for the increasing requirements with regard to the datatransmission capacity of switching devices lies in the constantlyincreasing demand for voice, video and data communication and theconsequence that networks of broader bands have to be used forestablishing connections. The cause for greater flexibility with regardto the number of subscribers which can be connected to switching deviceslies in the requirement for the infrastructure to keep pace technicallywith the flexibility of the business processes of the users of thecommunication device. This results in a great demand for flexiblemodularly expandable private branch exchanges.

Current devices are based on time-slot multiplexing connections betweencommunication terminals which are set up by means of a switching unit,for which purpose commands which indicate which defined time slot of anincoming connection is assigned to which defined time slot of anoutgoing connection are generated by a control device. Such switchingunits are generally suitable for the establishment of a defined numberof connections. The number of these connections is in this casedependent on the current demand of a private branch exchange. It isgenerally in the range of at most several thousand incoming and outgoingconnections. Consequently, such devices are not particularly well suitedfor flexible adaptation to growing numbers of subscribers. Similarly,the data transmission capacity per time slot of a connection isrestricted by the ISDN standard (Integrated Services Digital Network) toa maximum of 64 KB. This specified limit hinders, or prevents, aflexible subscriber-specific adaptation of different data rates for eachconnection.

Moreover, in the case of current devices, the setting-up of acommunication infrastructure in the form of a network of decentralizeddevices which are supplied with messages by a central control isrestricted because strict time requirements have to be satisfied whentransporting control messages and, as from a defined length of thecontrol line, it is no longer possible to comply with them. Used atpresent on these message lines is the HDLC protocol (Highlevel Data LinkControl), with which messages are transmitted with the function, forexample, of controlling the access of individual units in thedecentralized devices to a PCM data stream (Puls Code Modulation), inthat they prescribe defined time slots. If HDLC connections were simplylengthened, the time requirements between the communication partnersinvolved at the end of the link cannot be satisfied. The communicationpartners would have to be modified in such a way that they impose lowerrequirements on the time response. This is not practicable, since manypossible communication partners are concerned and consequently greatexpenditure is incurred and the communication partners would have to beprovided with more resources, for example memories.

FIG. 1 shows an example of a known private branch exchange 150 with acentral control device. This private branch exchange is connected to twoperipheral devices P1 and P2, to which there is respectively connected acommunication terminal KE1 and KE2 operating on a digital or analogbasis. These peripheral devices P1 and P2 are accommodated in the samespatial area as the first central device Z1. They are consequentlylocated in the same space or in the same cabinet as it. The terminalsoccupy defined time slots of a PCM data stream (Puls Code Modulation)with communication data. In this case, these analog or digitalcommunication terminals KE1 and KE2 are connected via interface modulesSLMO1 and SLMO2, which feed to the PCM data stream, or remove from it,data which are intended for the respective terminals, or come from therespective terminals, via time slots established by control messages.Two PCM data streams are denoted in the figure by 100 and 200,respectively. Likewise represented are signaling connections 110 and210, via which message traffic with a central control can take place. Inthe case of this representation it should be noted that a logicalrepresentation of the connections is shown in the topology forindividual connections, and that this is not a physical representation.In the technical realization of these networks, the transport data andthe messages can be transmitted over the same connection medium withoutrestriction.

Also represented are peripheral devices P1 and P2, and also the supplymodules LTUC1 and LTUC2, which regulate the data traffic to theinterface modules, for example SLMO1 and SLMO2, of the respectiveperipheral devices. In this case, the peripheral device is fed controlmessages via the line 110 and the peripheral device P2 is fed controlmessages via the line 210. It can be clearly seen in the case of thisknown private branch exchange that, with this arrangement of theindividual components of the switching device, both the information tobe transported and the signaling information, exchanged by means ofcoordinated message traffic, have to be fed to a central device ZE1.

To be specific, messages 2, which are to be exchanged between thecentral device ZE2 and the peripheral devices P1, P2, are collected anddistributed by a message device DCL. The setting-up and clearing-down ofconnections is controlled by means of the Call Processing CP, with theCall Processing using for this purpose, for example, device-specificinterface functions DH, which are realized for example in the form ofprogram modules. In particular, setting commands 1 for the switchingunit MTS are generated. Such a setting command essentially controlswhich input of the switching unit is to be connected to which output inorder to provide a communication connection via this switching device.In such a known communication arrangement, control and connectionfunctions are consequently performed by a single spatially integratedfunctional unit of the communication network. In the case of such acenter-oriented configuration, problems arise because the data to betransported have to be fed to the central device ZE1. This is the caseeven if, for example, two communication terminals which are connected tothe same peripheral device P1 want to communicate with each other. Sucha centrally oriented arrangement also gives rise to high expenditure oncabling, because both the control lines and the communication lines haveto be routed to the central device ZE1. It is not possible forperipheral devices to be distributed over a wide area, because thetime-critical message traffic via the control lines with the aid of aHDLC protocol cannot take place over links comprising lines of anydesired length. To be able to achieve a greater area coverage by meansof such devices, the coupling of a number of devices would beconceivable, although the advantages of a single system in the form ofcentral interfaces, and for example central facility control, would belost. Furthermore, when linking them up, additional trunk modules wouldhave to be installed and additional connecting cables would have to belaid for their connection. Such private branch exchanges also cannot bemodularly expanded to whatever extent is desired, because the switchingunit MTS for example can only be provided as a complete unit. This meansthat, in an extreme case, a new switching unit with, for example, 4096ports must be purchased and installed for a single additionalconnection. The transmission rate in such systems is limited for exampleby the possibility that only a maximum of 64 kbits, or some otheradministratively fixed or technically dictated volume of data which isprescribed by the ISDN standard, can be transmitted per time slot. Inthis case, different data rates for individual communication connectionsare not possible.

SUMMARY OF THE INVENTION

The invention is based on a method and an arrangement for couplingmessages of a central control device with a decentralized communicationdevice which are not subject to any restrictions with regard to thedistance between the central device and the decentralized device.

In one embodiment of the invention, the time-critical message traffic isensured in a particularly advantageous way by an especially suitablecommunication protocol on just one partial connection link. On a furtherpartial connection, in particular a long-distance connection, another,specifically suitable, communication protocol can then be used. Thisadvantageously achieves the effect that already existing modules indecentralized devices can continue to be used, without the length of theconnecting lines to a central control device being subject torestrictions. Similarly, the message transport is advantageouslyoptimized, because the messages are just transported directly and sothere is no longer the additional computational effort which would arisewhen one protocol is packed into another protocol. Similarly, fewer datatherefore have to be transmitted, whereby time advantages and higherdata capacities in message transport are attainable.

Standardized communication protocols, set up in accordance with the OSIlayer model (Open Systems Interconnect), are advantageously used,because standardized devices (chips, protocol stacks) for such protocolsare available on the market, making it easily possible to meet therequired increase in the transmission performance on a connection byusing faster devices. Since the messages themselves are transmitted oneach partial connection link, in an optimum way the volume of user datais transmitted and the data transmission structures can remainrestricted to the necessary minimum.

In the case of a first protocol, the HDLC method is advantageously usedon a lowermost layer level, because in this way the modules in thedecentralized devices, which today already have an HDLC interface, cancontinue to be used. This HDLC method is advantageously combined with asecond communication protocol, which on the lowermost layers either hasan Ethernet protocol or transmits there in accordance with the ATMprotocol. In this way it is possible to use networks that areestablished and available for long-distance transmission, it beingpossible as from layer 3 to use the same protocol layers again for thenetwork switching and transport, in spite of the different fundamentals.For this reason, mixed configurations of a wide variety of protocols andnetworks can also be set up without any technical development effort.The ATM transmission method is advantageously particularly suitable foruse on a long-distance connection, because different transmissionqualities can be set up on the connections, allowing defined timerequirements to be met in the message traffic.

In one aspect of the invention, the Internet protocol is advantageouslyused on the network layer, because this Internet protocol is alreadyavailable for a wide variety of transmission media, and consequently thesame transport and network switching services can be used for thevarious transmission media.

In another aspect of the invention, control messages are advantageouslytransmitted, because in this case there are hard time requirements ofthe communication partners, according to the method describes no changesare required in the decentralized devices, transmission methods forcontrol messages already exist for the HDLC method, because they havealready been implemented in the case of current devices, and because awide variety of networks can be used for the long-distance connections.

One embodiment of the invention is advantageously suitable for thecoupling of a number of decentralized devices to a central control,because messages are collected coordinated and distributed in adecentralized manner and have to be transmitted in a bundled manner on aline to the centre. In the bundling, a number of messages can beadvantageously packed into an IP packet and consequently theadministrative effort of the protocols can be reduced. The ratio of userdata to protocol data is better as a result, and consequently there is areduced load on the network.

For the administration of a number of decentralized devices, it isadvantageously possible to set up groups, for which messages arerespectively collected and distributed, because in this way messagecollecting and distributing devices which can already be used forcentral devices of a known type can be used in decentralized devices.

For the case in which a number of groups of decentralized devices areadministered, a sorting of the messages is advantageously carried out inthe central control device before they are processed, because in thisway a unique group-specific prioritizing and processing of the messagesis made possible.

At least two types of connecting lines, on which different transmissionprotocols are implemented, are used advantageously in an arrangement forcoupling messages between a decentralized device and a central controldevice. For the exchange of messages in the local exchange area,HDLC-based protocols are advantageously used, because in this wayalready known and existing decentralized devices on the basis of theHDLC protocol with their critical time requirements in decentralizeddevices can continue to be used, and Internet connections or ATMconnections, for which standardized products are established on themarket, can be used for the long-distance connections of thesedecentralized devices to the central control device, so that, withregard to the transmission capacity, a broad spectrum can be easilycovered by the acquisition of products generally available on themarket.

Depending on the required transmission capacity and distance, variousmedia, which are available for the most diverse networks, can beadvantageously used for the long-distance connections. For this reason,in the case of a number of decentralized devices, mixed configurationscomprising a wide variety of transmission media are also possible.

In another embodiment of the invention, first communication connectionsadvantageously take the form of a backplane bus, because in this wayalready existing modules can be taken over unchanged from conventionaldevices into new devices as decentralized devices. Likewise, this typeof configuration requires less additional development effort for thedevelopment of decentralized devices.

The protocol conversion takes place advantageously in the area of adecentralized device, because in this way the time-critical transmissionin accordance with the HDLC method can be best ensured. Similarly, thereis no need for additional devices which carry out a protocol conversionin the area of the private branch exchange. Moreover, converting devicesarranged decentrally in this way are also able to be adapted exactly intheir conversion capacity to the communication volume of the respectivedecentralized device, and consequently can be used particularlyefficiently.

A special device, which sorts and distributes messages which arereceived by it from various second decentralized devices, or are to besent to the latter, is provided advantageously in the central controldevice for the administration of second communication connections. Inthis way, a defined message processing over a number of decentralizeddevices is ensured and the possibility that messages over a number ofdecentralized devices can also be processed in a prioritizable manner isadvantageously ensured.

For the case in which the second communication connection is formed asan ATM network, the central control device is advantageously dividedinto two units; of which one has an ATM access, while the other may beconnected to this unit via a current Ethernet connection. This type ofconfiguration has the advantage that customary central control devicescan continue to be used largely unchanged and do not have to be furtherdeveloped for access to an ATM network. Furthermore, the ATM network canbe used for the transmission both of control messages and for thetransport of communication data between the terminals, only the Internetprotocol having to be implemented on layer 3 of the communicationprotocol for the transmission of the control messages, and the transferto the central control device to the Ethernet can also take place onthis layer. It is consequently possible to dispense with Ethernetconnections between the central control device and the decentralizedcommunication devices. It should be noted here that the network topologyfor the transport of communication data may well differ from the networktopology for the exchange of messages. The user of the communicationsystem has the advantage that he only has to have an ATM networkconnection, and not also an Ethernet connection.

The message processing takes place advantageously in the second centraldevice, because in this way previously customary peripheral devices canalso be involved in the message control sequence, so that a mixture ofpreviously customary devices of a private branch exchange with noveldevices of a new private branch exchange can be operated and controlledin any desired form. In another embodiment of the invention, controlmessages for the connection control of a switching unit are generatedadvantageously in the central control device and transmitted to thesecond decentralized communication devices, or are used for controllingthe switching unit in the case of mixed arrangements. In this way,connections can be established in the entire area of the switchingdevice, irrespective of whether the communication subscribers areconnected to novel devices or to customary devices.

BRIEF DESCRIPTION OF THE INVENTION

Exemplary embodiments of the invention are explained in more detailbelow on the basis of figures:

FIG. 1 shows a conventional communication arrangement.

FIG. 2 shows an example of a communication arrangement withdecentralized devices.

FIG. 3 shows a network structure comprising a central device and anumber of decentralized devices.

FIG. 4 illustrates the linking of a decentralized device to a centraldevice.

FIG. 5 illustrates an advantageous configuration of an arrangement forcoupling messages on the basis of an ATM network.

FIG. 6 shows a view of a detail of the coupling of decentralized devicesto a central control device via an ATM network.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows an example of an arrangement for setting up, clearing downand operating communication connections via decentralized devices whichare controlled by a central device. Here, for example, a private branchexchange 250 is represented. The same component parts of the device aredenoted by the same reference numerals in FIG. 2 as in FIG. 1. It isnotable in the case of this communication arrangement that there are aseparate transport network 700 and an independent control network310/410. Such a setup of an exchange has the advantage that alreadyexisting networks, in the form of public or private networks, can beused for the transport network. What is more, the control network has tobe routed to the central device ZE2.

The digital or analog communication terminals KE1 and KE2 arerepresented in this representation in such a way that they arerespectively connected to interface modules SLMO1 and SLMO2. Withoutrestricting the invention, however, such terminals which can beconnected to the transport network 700 directly, bypassing the interfacemodules SLMO, are also conceivable and able to be integrated in such anarrangement 250. Consequently, ATM terminals or IP-based (InternetProtocol) terminals can also be directly connected.

As can also be seen, the decentralized devices DZ1 and DZ2 in each casehave decentralized switching devices CS1 and CS2, which may for exampletake the form of ATM access devices. Similarly, it can be directly seenthat the switching unit MTS0 is no longer used for connection tasks.These connection tasks are instead undertaken by the transport network.

For controlling the decentralized switching devices CS1 and CS2, atleast one item of control information is in each case transmitted bymeans of a dedicated message to these switching devices via the controllines 410 and 310, which are component parts of a control network, forsetting up and clearing down the communication connection. This controlinformation includes time-slot-related control information, derived fromthe control instructions for the switching unit MTS. Furthermore, thefigure reveals that a conversion from PCM data into ATM cell data iscarried out on a data link 300 or 400. It should be noted here that theuse of an ATM network as a transport network serves here merely as anexemplary embodiment. Internet and other IP connections, or even TDMconnections, likewise come into consideration as transport networks. Theselection of the respective network is in this case dependent on theintended use and extends over the entire spectrum of available networks,both in the narrowband range and in the broadband range.

Because the communication connections to the central device ZE2 are nolonger needed in such arrangements, in the case of this configuration itis not necessary for connection fees, for instance for both connectionsfrom DZ1 and DZ2 to the central device ZE2 via public lines, for examplefixed lines, to be paid, as previously the case with a remote peripheraldevice PE in a device 150 from FIG. 1 when there is communication fromPE1 to PE2. For controlling the setting-up of the connection and theassociated exchange of messages, a transport-network-dependent callprocessing is carried out on the decentralized switching devices CS1 andCS2, but is restricted essentially to basic call functionality. Thefacilities are in this case realized and provided by the central controlZE2. Connections between the various central devices are controlled bythe central devices ZE2 by means of messages which contain controlinformation.

The advantages of such an arrangement are that it is capable of bothnarrowband and broadband operation. A possibly used backplane in thedecentralized device would have to be newly developed, however, in orderto allow broadband connections to be established, in contrast to TDMbackplanes. Furthermore, the transport network can be set up both onpublic networks and on private networks, or else on a mixture of thetwo. Furthermore, there is the possibility of assigning to the centraldevice ZE2 decentralized devices that are an unlimited distance away, sothat even very large installations can be provided with such a privatebranch exchange, which in turn serve for supplying widespread areas withcommunication connections. In this case, because a central device isretained, there is the possibility of continuing to use already existingsoftware, with minimal changes, for the control. On the other hand, newmethods of control would have to be developed and a new mechanism forensuring consistency of a distributed database would have to be createdif the control, like the switching unit, were likewise distributed. Afurther advantage of such a device 250 in comparison with networkedsystems of the type 150 is that the distributed system behaves like asingle telephone switching device and therefore facilities which aremerely implemented across the exchange can be operated there. Thisdispenses with the need to convert individual facilities to make themable to operate on a network. For this reason, central interfaces andapplications can likewise continue to be used.

FIG. 3 shows by an example, in a schematized form, the setup of aprivate branch exchange 450. There can be seen a central control deviceZE2, which is in connection with second decentralized communicationdevices DZ1, DZ10 and DZ20 via second communication connections 1001,1010 and 1020. These connections are generally long-distanceconnections, with which the less time-critical coupling of various firstdecentralized communication devices can be accomplished. It is indicatedby the dots between DZ1 and DZ10 in the figure that any number ofdecentralized devices DZ can be connected via second communicationconnections to the central device. Examples of such networks forlong-distance connection which may be given are ATM networks, Ethernets,or other IP-transporting networks. Assigned to each second decentralizeddevice are first decentralized devices. These second decentralizeddevices are in contact with the first decentralized devices via a firstcommunication connection. The message traffic from the firstdecentralized device to the second decentralized device is handled viathis communication connection, which at the same time serves as a relaystation for the communication with the central control device ZE2.

Connected to the second decentralized device DZ1 are first decentralizeddevices DZ12, DZ15 and DZ19, each via first communication connections2012, 2015 and 2019. The dots between the first decentralized devicesDZ12 and DZ15 are intended to indicate that it is possible within thelimits of the technical possibilities of a second decentralized devicefor any number of such first decentralized devices to be connected tothe latter via respective first communication connections. Furthermore,connected to the second decentralized device DZ10 are firstdecentralized devices DZ102, ZD105 and DZ108 via first communicationconnections 2102, 2105 and 2108. The functionality of the seconddecentralized devices for the message traffic is essentially identical.For the exchange of messages with the central control device ZE2, firstdecentralized devices DZ202, DZ207 and DZ237 are connected to the seconddecentralized device DZ20 via first communication connections 2202,22207 and 2237. In a favorable configuration of an arrangement, thefirst decentralized devices DZ12 to DZ 237 are configured as interfacemodules for communication terminals SLMO. The first communicationconnections 2012 to 2237 to the respective first decentralized devicesare generally connections via which time-critical control messages aretransmitted. For this purpose, the HDLC method is used between the firstdecentralized device and the second decentralized device as the firstcommunication protocol. These first communication connections mayadvantageously take the form of a backplane bus of a seconddecentralized device. This variant of the configuration allows moduleswhich are used in conventional systems 150 for the connection ofcommunication terminals to be used as first decentralized devices.

The second decentralized communication devices are connected overrelatively great distances, via LANs (Local Area Networks) or WANs (WideArea Networks) such as Ethernet or ATM connections for example, to thecentral control device ZE2. On these second communication connections, alayer protocol of the ISO type (Open Systems Interconnect) of protocolis implemented, comprising seven layers, the lowermost layerrepresenting the physical layer, the second layer the link layer, thethird the network layer, the fourth the transport layer, the fifth thesession control, the sixth the data presentation and the seventh theapplication layer. In this layer protocol, standardized in accordancewith ISO IS8802, each layer uses the services of the layer lying underit. Messages which are transmitted with the aid of this layer protocolconsequently receive additional information successively at each layer,thus producing a data structure in which the original message has sevenlayer-specific elements of information added to it. This process is alsoknown as “packing” the information, whereas the reverse process, inwhich the corresponding elements of the structure are returnedlayer-dependently to the respective layers to produce the originalmessage, is known as “unpacking”. Theoretically, the possibility ofinterleaving a number of such protocols would also exist, but wouldnecessitate a considerable administrative effort and would lead toincreased loading of the second communication connection during the datatransmission, because the information on the layer organization of theother protocol has to be additionally transmitted along with the actualmessage itself.

For converting the HDLC protocol used on the first communicationconnection into the OSI protocol layers used on the second communicationconnection, for example in the form of the layer sequencesEthernet/IP/TCP or ATM/IP/TCP, there is in a respective seconddecentralized device DZ1 to DZ20 in each case a device for protocoltransformation of the messages to be exchanged, this device in each caseperforming the conversion by unpacking the message completely from theprotocol used and then packing it into the other protocol and passing iton. As the figure further reveals, various first decentralized devicesand second decentralized devices form groups. These groups are deviceswhich are spatially close together and may, for example, be accommodatedin different buildings, which are connected to one another by a privatebranch exchange. For administering the message traffic from the firstdecentralized devices to the central control device, in the seconddecentralized device there is provided a message collecting anddistributing device, which acts virtually as a representativecommunication partner of the first decentralized devices and coordinatesthe message traffic between the central control device and the firstdecentralized devices.

Previously customary peripheral devices are also linked to ZE2 via adevice DCL (not represented). An additional software module decideswhether messages are sent as before via DCL or via the IP path andconsequently via the Ethernet connection. In the opposite direction,this software similarly forms both inputs (DCL and IP) in one.Consequently, the additional software module provides a uniforminterface in the direction of the system software and covers the splitinto two different paths and types of transmission.

In connection with the reference numerals which are used in the variousfigures, it must also be noted that the same reference numerals alsoconcern communication devices or component parts of communicationarrangements of the same type. The second communication connections tothe central control device may be configured on a wide variety ofcommunication media, it being possible for the Internet protocol to beused on layer 3 and the Transmission Control Protocol TCP to be used onlayer 4. Various mixed variants are conceivable here. This protocolstructure achieves the effect that, as from layer 3, messages can beexchanged over a wide variety of communication media system-wide.

FIG. 4 shows a view of a detail of the private branch exchange 450 whichis represented in FIG. 3. To illustrate individual elements of thesecond decentralized device DZ1 and of the central control device ZE2.As can be seen, a first communication connection KV1 is configured forexample as a backplane bus of a second decentralized device DZ1, thefirst communication connections 2012 to 2019 run there. In adecentralized switching device CS1 there is provided a conversion deviceHDLC1, IP1, which converts the HDLC protocol used on the firstcommunication connection KV1 into the OSI layer protocols used on thesecond communication connection 1001, and vice versa. The decentralizedswitching device CS1 has a port 700 to the transport network. For thecoordination of the message traffic between the first decentralizeddevices and the central control device there is in the seconddecentralized device DZ1 a message collecting and distributing deviceHDLC1. There, messages from first decentralized devices are collectedand passed on in a bundled form via the second communication connection1001 to the central control device ZE2. In the reverse direction, thecontrol messages arriving from the central control device aredistributed to the respective addressees in the second decentralizeddevice. To be able to evaluate and process in a coordinated manner thevarious messages which are sent to the different second decentralizedcommunication devices, or which are sent in the opposite direction fromthe various second decentralized communication devices to the centralcontrol device ZE2, there is in the central control device a connectiondevice IP2, which is capable of evaluating the protocol information onthe second communication connection 1001 and recreating the originalmessages, or packing them in the reverse direction. The connectiondevices IP1 and IP2 may in this case operate on the lowermost layerswith the Ethernet protocol. This connection device is in connection witha message processing and control device DCL2, which in the case of thecentral control device ZE2 possibly prioritizes, sorts, passes on forprocessing or sends messages also arriving from peripheral devices viaDCL, or sent from it.

As can be further seen, in the arrangement represented the switchingunit MTS no longer performs any function. However, it is conceivablethat a peripheral device, which is represented in FIG. 1, is connectedto ZE2 via a decentralized switching device of the same type as CS1, themessage traffic with ZE2 continuing to be handled by means of HDLC viaDCL and DCL2. In this way, conventional, already operating privatebranch exchanges can be combined with exchanges of a newer type and thistype of arrangement is appropriate as a migration solution for atransitional period of time. For the case in which older devices of thetype of a switching device 150 are connected, the switching unit MTS isstill required in order to perform the connecting function in the areaof devices of the type 150. DCL2, as an additional software module,brings the two message paths via DCL and IP2 together and thus coversthe existence of two interfaces for the central control ZE2.

FIG. 5 shows a special embodiment of a private branch exchange 450, inwhich an ATM network is used as the second communication connectionbetween the central control device. In the case of this specialconfiguration of the arrangement, the same ATM network can be used forthe transport network 700 and for the accomplishment of the messagetraffic via second communication connections by means of the IPprotocol. In this case, the transport network 700 and the controlnetwork which is formed by the second communication connections 1020 to1001 may have a complete different logical structure.

This special embodiment is particularly favorable because it is possiblein this case to dispense with Ethernet connections to the seconddecentralized devices DZ20 to DZ1 and only a single networkinfrastructure has to be provided, for example in the form of an ATMnetwork. However, this type of physical coupling for the accomplishmentof the message traffic requires adaptation measures in the area of thecentral control device ZE2. For this purpose, the central control deviceZE2 is divided into two subunits EZE2 and ZZE2, which are connected toeach other by a connecting line Z2020. In this case, the connection tothe ATM network is established via the first central unit EZE2, whilethe message collection evaluation, processing and distribution takesplace in the second central device ZZE2. More details on this emergefrom the description of FIG. 6.

FIG. 6 shows a partial view of the private branch exchange 450 which isrepresented in FIG. 5. Here, the individual components of thedecentralized device DZ1 and of the first central unit EZE2 and of thesecond central unit ZZE2 can be seen. Realized in the seconddecentralized device DZ1, for example by means of a backplane bus, arefirst communication connections 2015 and 2012, via which a communicationof the first decentralized communication devices DZ15 and DZ12 with adevice HDLC1 takes place in accordance with the HDLC protocol.

For example, communication terminals are connected to these firstdecentralized devices. The device HDLC1 serves as a message collectingand distributing device, which terminates the HDLC protocol in thedirection of the communication terminals. The messages are passed to thedevice IP1, which serves for packing the messages into the Internetprotocol. HDLC1 and IP1 consequently form the converting device fromHDLC to IP. The IP packets are fed to an ATM access device ATM1 andconverted there into an ATM cell stream.

The conversion of the data which are transmitted in accordance with theInternet protocol into an ATM cell stream for the device ATM1 may takeplace either in IPM1 or in ATM1. The data connections I100 and I200represented are not necessarily lines in the physical sense butfunctional block interfaces, which may also be formed as softwareinterfaces, for a transfer in the memory for example.

Also represented is an internal connection function IVF, which allowsconnected terminals access to the transport network 700. These devicesare a component part of a decentralized switching device CS1. Themessage traffic takes place via a second communication connection 1001,which is formed here as an ATM connection. In the first central unitEZE2 there are the same components for a decentralized switching deviceCS3 as in the case of CS1, although they are marked with the prefix “Z”for differentiation, and they perform the same functions as thecomponents of the same type in the case of CS1. Here, however, aprotocol conversion of the Internet protocol via the ATM network to theInternet protocol on the Ethernet takes place. This happens in ZIP or inZETH. Information between these components is exchanged via an internalconnecting line Z100. The Ethernet interface module is linked to thesecond central unit ZZE2 via the second communication connection 2020 toan Ethernet access module ETH. By such an arrangement, the ATM access isdecoupled from the central control device ZE2. In this way, a secondcentral unit ZZE2 can be constructed in a way essentially similar to adevice ZE2, which was described in FIG. 2. It is consequently notnecessary to carry out elaborate changes in an existing system to enableit to communicate in accordance with the Internet protocol on an ATMnetwork. This property is provided by the first central unit EZE2. Whilein the case of known devices the polling of the first decentralizeddevice DZ15 and DZ12 was carried out from the second central unit ZZE2,this now takes place from a representative module HDLC1 in the seconddecentralized device DZ1.

1. A method for coupling messages of a central control device withdecentralized communication devices, comprising: setting up and/orclearing down a communication connection for the transport ofcommunication data which is performed by at least one first functionalunit of a communication network; controlling the connection functionwhich is performed by a second functional unit of the communicationnetwork, wherein the first and second functional units are spatiallyseparate from each other, message traffic occurs on at least two partialconnection links; different communication protocols are used on thepartial connection links; and a message is transmitted on the partialconnection link directly using a respective communication protocol, inwhich groups of a number of first decentralized devices and seconddecentralized devices are administered, in which messages occur from anumber of first decentralized devices, the messages are transmittedafter passing through a first partial connection link in a seconddecentralized device in a bundled form and on one second partialconnection link, and in which the messages from/to the seconddecentralized devices are initially sorted and then processed in thecentral control device.
 2. A system for coupling messages of a centralcontrol device with decentralized communication devices, comprising: atransport network for providing a communication connection; a controlnetwork for controlling the setting-up and/or clearing-down of thecommunication connection; a device to control the setting-up and/orclearing-down of a connection in the transport network by a controlnetwork, the device being spatially separate from the transport network;at least one first decentralized communication device to receive and/orissuing a message; at least one second decentralized communicationdevice to collect and/or distributing messages; a central control deviceto issue and receive messages; at least one first communicationconnection between the first and second communication devices; and asecond communication connection between the second decentralizedcommunication device and the central control device, the secondcommunication connection being formed as an Internet or ATM network, andthe first communication connection being formed as an HDLC-basedconnection, in which the first communication connection is formed as abus on a backplane.
 3. The system as claimed in claim 2, in which thesecond communication connection is formed as a coaxial cable or as anoptical waveguide.
 4. A system for coupling messages of a centralcontrol device with decentralized communication devices, comprising: atransport network for providing a communication connection; a controlnetwork for controlling the setting-up and/or clearing-down of thecommunication connection; a device to control the setting-up and/orclearing-down of a connection in the transport network by a controlnetwork, the device being spatially separate from the transport network;at least one first decentralized communication device to receive and/orissuing a message; at least one second decentralized communicationdevice to collect and/or distributing messages; a central control deviceto issue and receive messages; at least one first communicationconnection between the first and second communication devices; and asecond communication connection between the second decentralizedcommunication device and the central control device, the secondcommunication connection being formed as an Internet or ATM network, andthe first communication connection being formed as an HDLC-basedconnection, in which, for the case in which a number of secondcommunication devices are connected via a number of second communicationconnections to the central control device, at least one devicecoordinates the messages, which sorts the messages arriving on thesecond communication connection, which is connected to a device toprocess the messages.
 5. A system for coupling messages of a centralcontrol device with decentralized communication devices, comprising: atransport network for providing a communication connection; a controlnetwork for controlling the setting-up and/or clearing-down of thecommunication connection; a device to control the setting-up and/orclearing-down of a connection in the transport network by a controlnetwork, the device being spatially separate from the transport network;at least one first decentralized communication device to receive and/orissuing a message; at least one second decentralized communicationdevice to collect and/or distributing messages; a central control deviceto issue and receive messages; at least one first communicationconnection between the first and second communication devices; and asecond communication connection between the second decentralizedcommunication device and the central control device, the secondcommunication connection being formed as an Internet or ATM network, andthe first communication connection being formed as an HDLC-basedconnection, in which the second communication connection is formed as anATM network, the central control device has a first and a second centraldevice, a converting device is present in the first central device, forthe conversion between protocol layers of the Internet protocol via theATM network to protocol layers of the Internet protocol via theEthernet, and the first and second central devices are in connectionwith each other via an Ethernet connection.
 6. A system for couplingmessages of a central control device with decentralized communicationdevices, comprising: a transport network for providing a communicationconnection; a control network for controlling the setting-up and/orclearing-down of the communication connection; a device to control thesetting-up and/or clearing-down of a connection in the transport networkby a control network, the device being spatially separate from thetransport network; at least one first decentralized communication deviceto receive and/or issuing a message; at least one second decentralizedcommunication device to collect and/or distributing messages; a centralcontrol device to issue and receive messages; at least one firstcommunication connection between the first and second communicationdevices; and a second communication connection between the seconddecentralized communication device and the central control device, thesecond communication connection being formed as an Internet or ATMnetwork, and the first communication connection being formed as anHDLC-based connection, in which the second communication connection isformed as an ATM network, the central control device has a first and asecond central device, a converting device is present in the firstcentral device, for the conversion between protocol layers of theInternet protocol via the ATM network to protocol layers of the Internetprotocol via the Ethernet, and the first and second central devices arein connection with each other via an Ethernet connection, and in whichthe second central device has the device for processing messages.
 7. Thesystem as claimed in claim 5, A system for coupling messages of acentral control device with decentralized communication devices,comprising: a transport network for providing a communicationconnection; a control network for controlling the setting-up and/orclearing-down of the communication connection; a device to control thesetting-up and/or clearing-down of a connection in the transport networkby a control network, the device being spatially separate from thetransport network; at least one first decentralized communication deviceto receive and/or issuing a message; at least one second decentralizedcommunication device to collect and/or distributing messages; a centralcontrol device to issue and receive messages; at least one firstcommunication connection between the first and second communicationdevices; and a second communication connection between the seconddecentralized communication device and the central control device, thesecond communication connection being formed as an Internet or ATMnetwork, and the first communication connection being formed as anHDLC-based connection, in which the second communication connection isformed as an ATM network, the central control device has a first and asecond central device, a converting device is present in the firstcentral device, for the conversion between protocol layers of theInternet protocol via the ATM network to protocol layers of the Internetprotocol via the Ethernet, and the first and second central devices arein connection with each other via an Ethernet connection, and in whichthe central control has a device to control a switching unit for thecreation of time-slot multiplex connections, and the device is inoperative connection with the device to process messages.